1. Field of the Invention
The present invention relates to vehicle suspension systems and more particularly to a suspension system providing side to side vehicle leveling for off center vehicle loads.
2. Description of the Prior Art
Side biased vehicle payloads, that is, the loading of a greater weight to one side of a vehicle rather than the other, cause a conventionally suspended vehicle to list toward the side of the vehicle carrying the greater weight. Vehicle list can produce undesirable vehicle handling problems.
Certain types of loads produce a predictable, but intermittent, load bias. For example, liftable snowplows, wingplows and mixers frequently produce asymmetrical, intermittent loads when mounted to trucks. Such devices may vary in the load they impose with the use to which they are put, but they always bias load to the same side. For example, snowplows are frequently larger at one end than the other. When the plow is lowered much of the plow""s weight is supported directly by the ground, but when the plow is lifted, the side of the vehicle carrying the larger, heavier end of the plow is more heavily loaded than the side carrying the smaller end of the plow.
Air springs have been used in vehicle suspensions for a number of years. Where cost is not an object, air springs may be used for suspension adjacent every wheel position. Air spring extension is controlled by adding or removing air from the spring. By keying the addition or removal of air to a measurement of the extension of the spring (or a functionally equivalent measurement), spring extension may be kept constant. This allows complete, and independent height control of the vehicle, and automatically solves the list problem.
However, for reasons of cost, including the cost for air springs, an independent height control system and the expense required to redesign vehicles for air springs and to add auxiliary wheel positioning elements, many vehicles continue to be built with conventional springs, and leaf springs particularly remain commonly employed in trucks. There is no convenient way to adjust the spring rate of a leaf spring in the field to compensate for loading of the vehicle, much less uneven loading.
The prior art has partially addressed the problem of uneven loading of trucks which retain conventional leaf spring suspensions. By the addition of a single auxiliary air spring, positioned between a leaf spring and a vehicle frame side rail adjacent the wheel expected to be closest to the load, additional support for the frame may be introduced by adding air to the auxiliary air spring. Such an auxiliary spring need not be large enough to support the entire vehicle weight, allowing it to be smaller and the retention of the leaf spring avoids the need for a major redesign of the vehicle suspension. Since a smaller spring can be used, the expense of providing a spring capable of fully supporting the vehicle is saved.
The control of a single auxiliary air spring has been based on a simple measurement of the local change in spacing from the frame rail to the axle. Air is then added or exhausted to return the extension of the spring to its default spacing. Such an arrangement compensates for the extra load carried locally, but ignores the lesser, but possibly substantial additional loads carried by the remaining springs, particularly the spring disposed at the opposite end of the same axle. The result is that the vehicle list, while usually reduced in degree, still exists, but occurs on the opposite side of the vehicle.
It is an object of the invention to provide a vehicle leveling system.
It is another object of the invention to provide complete side to side leveling of a vehicle with respect to an axle using a single auxiliary air spring.
According to the invention there is provided an apparatus for leveling opposed sides of a vehicle over first and second coaxial wheels. Main springs support the vehicle above each wheel. An auxiliary, inflatable air spring is positioned to provide additional support to the vehicle above one of the wheels. Deflection of the main springs from a norm or index is indicated by movement of tie rods mounted from the wheels, axle, or base of the main springs relative to the locally suspended portion of the vehicle. One tie rod is directly linked to a free end of an equalizer lever whereby the equalizer lever moves in the same direction as the tie rod. The second tie rod is coupled to the remaining free end of the equalizer lever by a rotatable rod, whereby the appropriate end of the equalizer lever moves in the direction opposite to the tie rod. The equalizer lever is suspended at its center from an actuation lever for a valve used to control inflation and deflation of the auxiliary air spring. The actuation lever has a pivot axis fixed with respect to the suspended vehicle, so movement the center point of the equalizer lever results in movement of the actuation lever. The direction of movement of the actuation lever results in valve action to inflate or deflate the pressure in the auxiliary air spring. Once leveling occurs, the volume of the air spring is held constant.
Additional effects, features and advantages will be apparent in the written description that follows.